Question: The scale on a map is 1cm : 5km. If two cities are 8cm apart on the map, what is the actual distance in km between the two cities?
Explanation: The scale means that every 1cm on the map corresponds to an actual distance of 5km. A distance of 8cm on the map is the same as 8 $\cdot$ 1cm. The actual distance between the two cities is 8 $\cdot$ 5km, or 40km.